There currently exists no biventricular mechanical circulatory support system for patients with cardiac failure after open heart surgery. Mechanical left ventricular bypass of patients after cardiac surgery has been limited in almost all cases by biventricular failure. This proposal will study single and biventricular cannulae bypass in sheep with normal hearts, and hearts with induced failure. Hypotheses to be tested include: (1) Cannula bypass is compatible with normal cardiac and circulatory function; (2) Cannula bypass can support the circulation and allow recovery of life-sustaining myocardial function after induced failure; (3) Total left ventricular bypass allows faster and more substantial recovery from induced failure than partial left ventricular bypass; and (4) The hyperdynamic state observed during cardiac bypass is related to increased autonomic, sympathetic activity and abnormal blood volume regulation. Basic animal data will be obtained from single and biventricular bypass concerning: (1) The role of the right ventricle during left ventricular bypass and ventricular interdependence, if any; (2) Myocardial effects of partial and total cardiac bypass and ventricular decompression: (3) Time and quality of myocardial recovery from failure and cardiac bypass; (4) Effects of pulsatile versus nonpulsatile single and biventricular bypass; and (5) Regulation of blood volume.